The present invention relates to a printer and, more particularly, to a stencil printer of the type pressing a paper with a press drum or an ink drum around which a master is wrapped for thereby printing an image on the paper.
It is a common practice with a stencil printer, which is a specific form of a printer, to use a press roller as pressing means or print pressure device. Another conventional print pressure device uses a press drum for printing an image while forcibly peeling off the leading edge portion of a paper from an ink drum. The press drum has substantially the same outside diameter as the ink drum and is rotated at substantially the same peripheral speed as, but in the opposite direction to, the ink drum while clamping the leading edge portion of a paper. With the press drum, it is possible to prevent the leading edge of a paper from remaining on the ink drum without being removed by a peeler and thereby jamming a paper transport path. Further, the press drum reduces noise and enhances the registration accuracy of an image in the direction of paper conveyance. In the print pressure device using the press drum, a paper clamper is positioned in a recess formed in a part of the outer periphery of the press drum and clamps the leading edge portion of a paper fed to the press drum. The press drum presses the paper against the ink drum with the paper clamper clamping the paper, so that an image is printed on the paper. Subsequently, the paper clamper is opened in order to release the paper or printing. The printer is transferred from the paper clamper to a paper conveying unit.
The above paper clamper clamps the leading edge portion of a paper over several millimeters, generally 2 mm to 5 mm. At this instant, the paper clamper slightly bends the leading edge portion of the paper inward in the radial direction of the press drum, so that the clamper itself does not contact the ink drum. This kind of layout works satisfactorily so long as the paper to be clamped is an ordinary paper or similar thin paper. However, when the paper is a drawing paper, postcard or similar thick paper, the paper clamper cannot bend the leading edge portion of the paper radially inward unless it is sufficiently strong. As a result, the end of the paper clamper cannot be fully closed and hits against the master wrapped around the ink drum, ripping the master. Consequently, ink fed to the outer periphery of the ink drum is forced out via the ripped portion of the master and transferred to the paper clamper. This part of the ink smears the paper clamper and therefore the leading edge portion of the paper.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Utility Model Laid-Open Publication No. 61-198065, Japanese Patent Laid-Open Publication Nos. 7-17121, 4-329175, 8-59031, 5-330225, 8-332769, 9-1914, 9-216448 and 8-58216, and U.S. Pat. No. 4,911,069.